<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>背景色半透明</title>

    <style>
        body {
            background-image: url(../imgs/bgImg.jpeg);
            background-repeat: no-repeat;
        }

        div {
            width: 300px;
            height: 300px;
            background-color: rgba(0, 0, 0, .3);
        }
    </style>

</head>
<body>
    
    <div>123321</div>

</body>
</html>